Field
This disclosure relates to optical materials composed of nano-droplets dispersed in a polymeric solid. The nano-droplets may contain a liquid solution of a dye or other optically interactive material.
Description of the Related Art
Photochromic dyes are compounds that reversibly convert between two states or forms having different colors in response to stimulation with electromagnetic radiation. Typically, irradiation with light within a specific wavelength band causes isomerization or conversion from a relatively transparent form to a more colored or absorptive form. Once the irradiation by light is interrupted, the reverse conversion from the colored form to the transparent form may occur spontaneously through a thermal process. Alternately, conversion from the colored form to the transparent form may be induced or accelerated by irradiating at a wavelength different from that used for the conversion from the transparent state to the colored state. Photochromic dyes that spontaneously convert from the colored form to the transparent form are termed “T-type photochromes” and photochromic dyes that convert from the colored form to the transparent form in response to radiation are termed “P-type photochromes.”
The speed of isomerization between the two forms varies according to the wavelengths used, the temperature, the intrinsic properties of the photochromic dye, and the medium where the molecules of the photochromic dye are dissolved or dispersed. Generally, photo-induced conversions are the fastest. The speed of the spontaneous back isomerization from the colored state to the transparent state of T-type photochromes is slower and depends to a large degree on temperature and the medium in which the photochromic dye is dissolved or dispersed.
Available T-type photochromic dyes include, for example, various spirooxazines, azobenzenes, chromenes, and other photochromic systems able to interconvert back thermally through molecular conformational changes (e.g. dihydroazulene) or other mechanisms (e.g. viologens). For all of these families of photochromic dyes, the conversion between their two states requires a geometric and significant conformational change at the molecular level. These molecular changes are generally fast when the photochromic dye is in a liquid solution, where the molecules have a large degree of movement. On the other hand, the conversion speed, particularly for the spontaneous reverse conversion, is greatly slowed when these photochromic dyes are dispersed directly in a solid environment. This is a significant problem in many applications.
Throughout this description, elements appearing in figures are assigned three-digit reference designators, where the most significant digit is the figure number where the element is introduced and the two least significant digits are specific to the element. An element that is not described in conjunction with a figure may be presumed to have the same characteristics and function as a previously-described element having the same reference designator.